Repair ZP120

Your assumption seems correct. The PWM is not switching therefore no secondary voltages will show up. I would unsolder that PWM and watch the bulb go out!
If it’s too hard to get the PWM out in one piece, cut the leads and unsolder them one by one.

I removed the TO-220 PWM - and wouldn't you know... the bulb goes dim. 🙂 The part shows 30 ohms of continuity from pin 1 (GND) to pin 3 (Vcc) and 32 ohms from GND to pin 4 (FB). The continuity is in both directions. Based on the schematic, this part looks blown to me.

I think we may have found the culprit. Now I just need to find a replacement. It is a 5M0265R Fairchild. Looks like the replacement is a KA5M0265R.

Nobody carries some of these parts in the US, so I need a long wait from China (yes not Mouser or Digikey - seems to be special order). In the mean time I decided to probe around and have a small concern. The datasheet on the KA5M0265R states that the max VCC on this is about 30V. My testing on pin 1 (GND) and pin 3 (VCC) on the Sonos board for where the KA5M0265R goes shows 44V. So I am wondering if that is what may be blowing that? @gruv2ths, when you have a chance, can you post what VCC you get at pins 1 and 3 so I have a comparison?

I am reading 13V across pins 3 and 1. That is with the dim bulb installed so it is probably a little bit higher.

Is that with or without the PWM attached? Im wondering with the PWM attached, it may pull some of that voltage down. I am currently waiting on that PWM from China.

Yes that is with the PWM installed.

Cool... yeah, mine is with it removed. I'm reading 44V at 1 and 3 with a dim bulb as well. I bought a pack of 10 of the PWMs from China, so I have room in case of failure. I'm really hoping this is the bad component since my bulb is full dim after the caps charges and this PWM is removed. I'll post when I get them and try it out.

New PWMs and SCK 054 Thermistors finally came in from China. I replaced them and just as I thought, the PWM pulls down the voltage. Checked at 13.03V on pins 1 and 3 on the PWM 😉 Fired up the dim bulb and it went dark. Shut off the power and put the wifi cards back in. Moment of truth... fired it up again with the dim bulb... and the white LED flashed.

Waited a few minutes and opened the iPhone Sonos app. Bob is your Uncle! There it was in all its glory and works!

The Sonos lives and is revived. Total cost for replacement parts: $3.00. Total opportunity cost (I almost tossed it)... $500. Savings to fix it myself: $497.00. Priceless.

I want to personally thank @gruv2ths for the insight on this, and @chicks for the dim bulb ideas. That sent me on a Youtube and reading spree that gave me the tools and confidence to diagnose and fix the problems. Thanks for all the help!

'Bob is your Uncle!" Greatness.
Happy for you! Congrats!

Thanks. I would like to share a couple of items that may help others...

I have no idea what kind of solder that Sonos uses, but it is insane. In order to get it to melt, I had to get my Hakko iron up to 900 degrees. 700 (its default) would barely get it to melt. Getting it off components was a chore. That PWM and heat sink took a good 45 minutes to get off along with about 2 feet of desoldering braid. I am surprised I didn't destroy contacts as I really had to put that iron on for a while to get that solder to move. I tried a desoldering pen too, but to no avail. The best way to get it off was keep cracking at it with desoldering braid. I would love to hear if anyone has any hacks or ways to deal with such a problem.

Also, the dim bulb was brilliant. What a great tool to build. It is critical for testing any sort of power supply to keep you from blowing more components. Without this, I would have destroyed multiple resistors and thermistors that kept blowing. I built this for about $25 and you can get the parts at HomeDepot:

https://www.youtube.com/watch?v=rDe6oLKm-ao

This one was nice and clean to make - took about 10 minutes. This helped me trace the hot part. A 60 watt bulb seemed to do the trick for finding the failed component. I tried a 200 watt bulb and it let too much power through, so the bad components would get raging hot quickly. From my readings, the hot part is almost always the culprit for a failed component.

The best resource that I found for fixing and diagnosing power supplied is here:

http://www.electronicrepairguide.com/Smps-repair.html

The guy sells a PDF book that details everything from how to test different components to what tool to use. He has a nice chapter on a dim bulb tester. That site and doc really walks through the different sides of a power supply and what to look for. IMHO, that was invaluable.

Anyways, I really hope this helps others. This was a great learning experience and has given me the confidence to perhaps start hunting for bad Sonos products on eBay and fix em up. ;-)

Final words... I really want to encourage people to post in these forums for help. We CAN fix these things and with a great community like we have here, we can keep these things running. 🙂